In one form of a fluid pressure control valve, a flow control element, such as a spool or valve member, is movably positioned in a valve chamber for selectively fluidically coupling ports. The spool may be directly actuated by a movable armature or plunger. A solenoid controllably positions the plunger, which results in movement of the spool. Typically, a coil spring is used for biasing the spool to the neutral position.
One type of solenoid operated valve comprises a three position cartridge valve. A pair of solenoids, or a bi-directional solenoid, are selectively energized for positioning the valve member using a pull force or a push force between opposite actuated positions. Particularly, energization of the solenoid coil produces a force acting on the plunger to move the plunger in a direction toward the valve member, to provide a pushing action, or away from the valve member, to provide a pulling action. Such a valve may be used to operate double acting cylinders, in bi-directional motors, or the like.
With a four way valve, an elongate cylindrical valve housing has an axial through bore defining an interior chamber. A port end of the chamber comprises an end port. A plurality of axially spaced side openings define first, second and third side ports. The valve member selectively couples the end port and the side ports for selectively controlling fluid flow. In a typical application, the end port is connected to a tank. One of the side ports, typically the middle, is connected to a pressure source. The other side ports are connected to the controlled device. In the neutral position of the valve member, flow may be allowed through the center of the spool from the pressure source to the tank. When one of the coils is energized, the valve member is pushed or pulled to provide fluid flow between the various ports, depending on the particular configuration of the hydraulic circuit.
The spring chamber functions to hold the spool in the center or neutral position in a de-energized state and to return the spool to the center or neutral position after the coils are de-energized. As described above, mechanical or electrical forces applied to the plunger overcome the spring force and shift the spool into a pull or push position. External forces, such as flow forces, produce non-symmetrical loads. However, a conventional three position solenoid cartridge valve includes springs providing symmetrical holding or return forces for the push and pull operation.
The present invention is directed to solving one or more of the problems discussed above, in a novel and simple manner.